1. Field of the Invention
The invention relates to the field of light paths. A particular application of the invention relates to light paths for connecting optical measuring means situated in effluent coming from a well passing through underground formations, such as a well for oil, water, or the like.
2. Description of Related Art
Numerous light-path applications relate to devices in which the optical fiber(s) connected to the sensor(s) for measuring purposes are to be found in a medium which is wet or corrosive and in which temperature and pressure can be high, while the electronic equipment to which connection is made must necessarily be located in a medium which is dry, clean, and preferably under conditions of pressure that are close to atmospheric conditions. This problem of providing sealing between optical fibers and electronic equipment (placed in a protective enclosure) can be solved by using a leakproof fiber feedthrough at the boundary between the two media. French patent application No. FR 00/12250 filed on Sep. 25, 2000 in the name of the Applicant describes an embodiment of a fiber feedthrough adapted to such applications.
However a fiber feedthrough comprises an optical fiber that is stripped and inserted in a metal ferrule. Such feedthroughs are therefore fragile and relatively bulky if it is desired to pass a plurality of fibers, since each fiber must be inserted in a respective ferrule. Fiber feedthroughs are therefore very short and they are connected to the external measurement means and to the electronic equipment inside the tool via connectors situated on either side of said feedthrough. Unfortunately, connectors, which constitute mere couplings between two pieces of optical fiber, nevertheless also constitute an additional source of optical disturbances and faults, in particular because it is very difficult to join two fibers end to end without giving rise to losses in light transmission.
Furthermore, most prior art light paths make use of a component referred to as a “Y-coupler” situated between the fiber feedthrough and the means for emitting and receiving light. Such a component is Y-shaped and its function is to enable a single fiber extending between the feedthrough and the Y-coupler to convey light to a sensor (usually light from a diode or a laser) and to process the light returned by the sensor (usually by means of a photo detector). Nevertheless, since Y-couplers are manufactured using machining that is complex, and since they are generally intended for applications in ambient media, it is very difficult to adapt them to conditions of use at high temperature (i.e. greater than 150°). The reliability and the lifetime of the light path are severely affected thereby.
It is desirable to remedy those drawbacks by proposing a light path which provides the functions of conveying light to and from an optical sensor while minimizing light losses and faults.